Commenting on your friend’s check-ins is a friendly foray into messaging and it will give the app a more real-time vibe. But what I’m most excited for is the long awaited photo feature, which lets users attach photos to tips and venues like the best dishes at a restaurant or as a way to easily identify a hidden speakeasy. “Venue pages on your mobile device will pull up photos from past friend’s check-ins, providing that special feeling of digitally shared serendipity,” said Alex Rainert, Foursquare’s Head of Product.

In early 2011 users will have the ability to push those photos from Foursquare to Facebook, Twitter and Flickr. For now the digital diary of users’ Foursquare photos and comments will be stored on each individual’s Foursquare history page. This information will be particularly useful, say if you spent a week in Barcelona adding tips and snapping photos, and you want to export and share that week of information to a friend for his or her upcoming trip to Spain.

A little word about privacy: Photos attached to check-ins will only be visible to friends (unless you push these photos to other networks like Twitter), whereas photos attached to tips and venues will be visible to the Foursquare community. Comments are only viewable by your Foursquare friends and the comment receiver’s friends.

Photos and comments will launch on the Android app later next week, and on Blackberry in January 2011.